Structural changes in a protein fragment from abalone shell during calcium carbonate precipitation

Mineralized tissues grow up through biological controlled processes in which specific macromolecules are involved. Some of these molecules, present in very low concentrations and difficult to localize and characterize, become entrapped into the mineralized tissue. In this study a protein fragment, GP, obtained by the alkaline digestion of the green sheet of abalone shell, is used as a probe to study the changes in the molecular structure that occur during a precipitation process of calcium carbonate. This important goal was achieved by exploiting a fluorescent tag in GP. The experimental results obtained using spectroscopic, chromatographic and microscopic techniques indicate that GP controls the precipitation kinetics and the morphology of calcium carbonate crystals, and undergoes a structural reorganization only when entrapped into calcium carbonate crystals. To our knowledge this represents one of the first studies on the conformational changes of a protein fragment involved in biomineralization processes moving from the solution into the mineral phase.